This invention generally relates to systems and methods of leak detection and is specifically concerned with a system and method for locating a leak in the steam turbine components of a turbine generator.
Systems for detecting air inleakage in the steam. turbine components of an electrical generator are known in the prior art. Such turbine components are designed to operate in an atmosphere consisting of steam and the purpose of such systems is to locate air leaks in the housings that contain these components so that ambient air may enter the housings that contain these components. Such leaks may occur from, for example, a misassembly of the steam turbine components after a maintenance operation, improperly left-on valves, or the breaking down of seals in the system from thermal differential expansion. The prompt detection of any such leakage sites is important if the various expensive components of the steam turbine system are to realize their full life span, as the unchecked ingress of the oxygen and carbon dioxide components in ambient air results in increased feedwater and economizer corrosion, boiler tube failure, reduced thermal efficiency, and corrosion fatigue and stress corrosion cracking of turbine components.
Because of the potential damage that can occur to the steam turbine components as a result of excessive air inleakage, many utilities employ continuous monitoring systems that are designed to inform the plant operators when a leakage condition occurs in the steam turbine system of the generator. Such monitoring systems generally operate by continuously monitoring the total output flow of the gases exiting the vacuum pump that continuously exhausts the steam from the steam turbine system. Any significant increase in this flow indicates that an inleakage condition has arisen. However, once such a leakage condition has generally been detected, the plant operator must then find the exact location of the leak before a suitable repair operation can be performed.
In one of the most common prior art leak detection systems, the system operator connects a tracer gas detector to the output of the vacuum pump of the steam turbine system, and then proceeds to spray a quantity of tracer gas, such as helium or freon, at potential leakage sites around the housings of the various components of the steam turbine system. The amount of gas sprayed is only roughly regulated by the operator, who merely counts to himself while pulling the trigger of a pistol-shaped nozzle. When the tracer gas is sprayed around the site of an air leak, some of the tracer gas is sucked into the interior of the steam turbine system, where it is ultimately directed into the inlet of the tracer gas detector via the outlet of the suction pump. When the tracer gas detector indicates that it has received a significant amount of tracer gas through its inlet, the system operator knows that he has released tracer gas around the site of a leak in the turbine system.
While the aforementioned prior art leakage detection system is capable of fulfilling its intended purpose, the applicants have noted several areas where such systems could stand improvement. For example, whenever tracer gas is released at the site of a major leak, it is not uncommon for the tracer gas detector to receive such a large volume of tracer gas that its sensors immediately become saturated. This is not an unusual occurrence as such devices are typically capable of detecting a flow of helium of as little as 10.sup.-10 liter-atm/sec, and further because it is necessary to adjust the gas detector to a fairly sensitive level so that any significant in-leakage condition may be detected. Unfortunately, once the tracer gas detector becomes saturated, it frequently takes several minutes for the excess helium to clear out of the detector before it can again become sensitive to a relatively small flow of helium. Such a saturation condition substantially protracts the amount of time necessary to completely inspect all of the potential leak locations on a steam turbine system, and may occur whenever helium is sprayed in the vicinity of a large leak, or whenever the technician inadvertently sprays too much helium around the location of a more moderate leak. The latter situation is made possible by the fact that the amount of tracer gas discharged by the tracer gas source is not precisely regulated, but rather is a subjective function of how long the system operator chooses to squeeze the trigger of the helium spray nozzle. The spraying of an imprecise amount of helium also makes it impossible for the system operator to make any but the roughest estimate of how large the detected leak might be.
Clearly, there is a need for an improved system for detecting the location of a leak in the steam turbine system of a generator which avoids the substantial delays associated with the prior art by preventing a saturating flow of helium from entering the tracer gas detector of the system. Ideally, such an improved system would be relatively simple and inexpensive, and broadly adaptable to detecting leaks in a variety of devices. Finally, it would be desirable if the improved system were capable of providing an accurate determination of the size of the leak detected.